Influence of Plasma Expansion on a Spectral Line Decaying in an Ionizing Plasma in a Theta Pinch

Abstract

The particle end-loss process and its influence on the intensity of the HeII 468.6 nm line are investigated in a small linear theta-pinch plasma using spectroscopic techniques. In side-on measurement at the center of the plasma column, the HeII line intensity decreases with a much larger decay rate than in end-on measurement. The side-on decay rate is due to both the ionization and the particle-end-loss processes, while the end-on decay rate is mainly due to the ionization process. The difference between the two rates is investigated by solving rate equations involving both ionization and plasma expansion. Good agreement is obtained between the experimental and theoretical results. A simple method, using both the side-on and the end-on measurements is offered for estimating the particle-end-loss rate due to the plasma expansion.